In a drug delivery device a piston within a cartridge that contains a drug may be provided. The piston may be displaced with respect to the cartridge for delivering a dose of the drug from the cartridge. It is desirable that the dispensed dose of the drug matches the dose which was previously set by a user as good as possible. That is to say, the device should have a high dose accuracy. In particular, it should be avoided that a dose dispensing action may be triggered when the size of the set dose exceeds the quantity of drug present in the cartridge.
Drug delivery devices are described in documents WO 2008/031238 A1 and US 2007/0197976 A1.